1. Field of the Invention
The present invention relates to a solid-state image capturing device, and particularly, to a CMOS type solid-state image capturing device, a manufacturing method of the same, a driving method of the same, and an electronic apparatus using the solid-state image capturing device.
2. Description of the Related Art
A general CMOS solid-state image capturing device according to the related art uses a method of sequentially reading signal charges generated and accumulated in light receivers of pixels arranged in a two-dimensional matrix shape in every column. In this case, since exposure timing in the light receiver in each pixel is determined by initiation and termination of the reading of the signal charges, the exposure timing is different in every pixel. For this reason, when the image of a fast moving subject is captured using such a CMOS type solid-state image capturing device, a problem may arise in that an image obtained by capturing the image of the subject is deformed.
In order to solve this problem, a simultaneous image capturing function (global shutter function) of realizing simultaneous accumulation of signal charges has recently been suggested. Moreover, a CMOS type solid-state image capturing device having the global shutter function has increasingly been used.
In the CMOS type solid-state image capturing device having the global shutter function, the signal charges generated in a light receiver are generally stored until the signal charges are read. Therefore, a charge accumulator having a light shielding property is necessary (for example, Japanese Unexamined Patent Application Publication No. 2004-111590).
The exemplary configuration of the CMOS type solid-state image capturing device having the suggested global shutter function according to the related art will be described below.
(1) There has been suggested a CMOS type solid-state image capturing device in which an FD (Floating Diffusion) portion is used as a charge accumulator without providing a charge accumulator. In this case, the FD portion and a reading gate configured to execute transmission between the FD portion and a light receiver are shielded from light. In the CMOS type solid-state image capturing device with such a configuration, all of the light receivers are first reset. The light receivers are reset by a method of using the reading gate and the FD portion or a method of forming the structure of a reset gate and a drain of the light receiver. Subsequently, the light reception is initiated by turning off the reading gate, and the signal charges are transmitted from the light receivers by simultaneously executing the reading in the reset FD portions of all of the pixels upon terminating the light reception and by turning on the gate. Subsequently, the gate is turned off by transmitting and then reading the signal charges. Subsequently, the signal charges accumulated in the FD portion are sequentially read by a pixel amplifier and are output to the column circuit via a signal line. Since the light receiver can almost continuously receive light of the subsequent frame in the reading method, the reading method is used in many cases particularly when a video is captured.
In the above-described configuration, since a separate charge accumulator is not formed and the FD portion serves as the function of the charge accumulator, a simpler configuration can be realized. Therefore, the path area of the light receiver can be made larger. In the CMOS type solid-state image capturing device with such a configuration, leak current in the FD portion is larger by about 103 to 105 times than that of the HAD (Hole-Accumulation Diode) configuration (HAD: registered trademark) of the same area. For this reason, problems with an S/N ratio may arise in this configuration.
(2) There has been suggested a CMOS type solid-state image capturing device in which a charge accumulator is formed between a light receiver and an FD portion. In this case, a transmission gate is formed to transmit charges between the light receiver and the charge accumulator and a reading gate is formed to transmit charges between the charge accumulator and the FD portion.
In the CMOS type solid-state image capturing device with such a configuration, the light receivers are simultaneously reset in all pixels. Subsequently, photoelectric conversion and accumulation of the signal charges are simultaneously executed in the light receivers of all the pixels in the state where the transmission gates are turned off. Subsequently, by simultaneously turning on the transmission gates in all the pixels, the signal charges are transmitted from the light receivers to the charge accumulators. After the signal charges are transmitted, the transmission gates are turned off and the light reception period is terminated (or the light reception of the subsequent frame and the accumulation of the signal charges are continuously executed). Subsequently, the signal charges accumulated in the charge accumulators are read in the FD portions by sequentially turning on/off the reading gates.
The CMOS type solid-state image capturing device executing the accumulation and transmission has an advantage in which the degree of reading freedom is large and dark current is easily reduced. However, there are disadvantages in that a space is restrictive to guarantee both the accumulated capacity of the light receiver and the accumulated capacity of the storage capacitor in each pixel and it is difficult to guarantee the amount of charge.
(3) There has been suggested a CMOS type solid-state image capturing device having the configuration of (2) and an intermediate configuration of the configurations of (1) and (2) in which the method of transmitting the signal charges is changed. In this transmitting method, the signal charges subjected to the photoelectric conversion are transmitted from the light receiver to the charge accumulator during turning on the transmission gate and the signal charges are accumulated in the charge accumulator. The signal charges accumulated in the charge accumulator are read in the FD portion in line order by turning on/off the reading gate.
In the transmitting method, since the transmission gate is turned on during the light reception, there is a disadvantage in that dark current easily occurs from an insulating film below the transmission gate and a silicon interface.
In order to realize the CMOS type solid-state image capturing device according to the related art, problems may arise in the light shielding property of the charge accumulator, a saturation charge capacity (Qs) of the charge accumulator, an aperture ratio of the light receiver, the Qs of the light receiver (type of accumulation of the signal charges in the light receiver), and the like.